This invention relates to an automotive wheel bearing assembly and a method for manufacturing the same.
Among automotive wheel bearing assemblies, there are ones for driving wheels and ones for non-driving wheels. As an example, a wheel bearing assembly for a driving wheel is shown in FIG. 10. It comprises an outer member 3 having two raceways 3a, 3b on its inner peripheral surface, an inner member 1 having raceways 1a, 1b opposite the respective raceways 3a, 3b, and rolling elements 8 disposed between the outer member 3 and the inner member 1 in two rows. A wheel-mounting flange 2 is provided on the outer member 3 or the inner member 1. In the example shown in FIG. 10, the wheel-mounting flange 2 is formed on the inner member 1 having a spline hole 9 for a drive shaft in inner periphery thereof.
A brake rotor 20 is fixed by bolts 18 to the side 2a of the wheel-mounting flange 2 of each device. But after assembling, if there should be a runout of the brake rotor 20, with increasing speed of cars, brake vibrations may occur during braking, or brakes may be worn unevenly. Depending on the degree of runout, brake vibrations may occur even at low speeds.
Heretofore, in order to minimize such runout of the brake rotor 20, adjustment of e.g. phase of the bolts which were pressed into the wheel mounting flange 2 with respect to the bolt hole of the brake rotor 20 was necessary. Such a work is troublesome and poor in workability.
Also, if the outer raceway 1a is directly formed on the inner member 1, it is necessary to form a hardened layer 21 on the raceway 1a. Thus, the outer peripheral surface of the inner member 1 is hardened by heat treatment.
Heretofore, when the outer surface of the inner member 1 is heat-treated, a heat-affected layer of the hardened layer 21 on the raceway 1a extends beyond a seal land portion 22 and reaches bolt holes 11 for hub bolts 7 formed in the wheel mounting flange 2.
But, if there exists a heat-affected layer over such a wide range, when the hub bolts 7 are pressed into the bolt holes 11, strain will act on (i.e. distort) the wheel mounting flange 2. This increases the runout of the wheel mounting flange.
If the runout of the wheel mounting flange is large, the brake rotor 20 fixed to the side face 2a by bolts 18 tends to runout. This may cause brake judder and abnormal sound.
An object of this invention is to prevent vibrations and uneven wear of a brake resulting from runout of the brake rotor caused with an increase in the car speed, and to provide a reliable wheel bearing assembly which needs no troublesome runout adjustment when mounting the brake rotor.
Another object of this invention is to provide a wheel bearing assembly which minimizes runout of the wheel mounting flange to prevent brake judder and abnormal sounds.
A still another object of this invention is to provide a constant-velocity joint mounted in a wheel bearing assembly for a driving wheel which is reliable and prevents stick-slip sound.
According to this invention, there is provided a wheel bearing assembly comprising an outer member having two raceways on inner peripheral surface thereof, an inner member having raceways formed thereon so as to be opposite to the two raceways, and rolling elements arranged in two rows between the outer member and the inner member, one of the outer member and the inner member being formed with a wheel mounting flange, a brake rotor being mounted on one side of the wheel mounting flange, characterized in that the maximum runout variation of the one side of the wheel mounting flange is restricted within a predetermined value when one of the outer member and the inner member that has a wheel mounting flange is rotated with the other fixed.
By this arrangement, troublesome adjustment of runout of the brake rotor after it has been mounted becomes unnecessary.
In the above arrangement, by restricting the maximum variation of runout of the side face of the wheel mounting flange to 50 xcexcm, reliable assemblies are obtained.
By restricting the maximum runout variation per cycle of runout within a predetermined value, it is possible to suppress runout of the brake rotor. The predetermined value is preferably 30 xcexcm.
Further, if the frequency of runout per revolution is equal to the number of wheel-mounting bolts multiplied by an integer, or if the number of wheel-mounting bolts is equal to the frequency multiplied by an integer, it is possible to make more uniform the deformation of the brake rotor due to tightening force of the mounting bolts between the peaks of runout of the brake rotor mounting surface against which the brake rotor is pressed, thus preventing increase of runout due to deformation of the brake rotor. The mounting position of the wheel-mounting bolts may not necessarily coincide with the positions of the peaks or valleys of runout of the brake rotor mounting surface.
The wheel mounting flange may be formed integral with the inner member.
A drive shaft may be mounted in the inner member, or the inner member may be formed integral with the outer ring of a constant-velocity joint.
Restriction of runout of the side of the wheel mounting flange may be carried out with reference to the axis of rotation of the inner member or outer member having the wheel mounting flange before it is assembled, or may be carried out by rotating the wheel mounting flange with the wheel bearing assembly assembled.
According to this invention, at least one of the raceways formed on the inner member on the side near the wheel mounting flange is formed directly on the inner member, and a heat-affected layer of a hardened layer formed on the raceway on the side near the wheel mounting flange is restricted so as not to reach holes for hub bolts formed in the wheel mounting flange.
If the heat-affected layer of the hardened layer does not reach the bolt holes for hub bolts in the wheel mounting flange, it is possible to prevent deformation of the wheel mounting flange. Thus the runout of the wheel mounting flange can be suppressed to a minimum.
By adjusting the depth of the hardened layer at the raceway to 0.7-4 mm at the deepest portion, and the depth of the hardened layer at the seal land portion to 0.3-2 mm at the deepest portion, it is possible to prevent the heat-affected layer of the hardened layer from reaching the bolt holes.
According to the present invention, a brake rotor fixing surface on one side of the wheel mounting flange is finished to finer surface roughness than the other side. By fixing the brake rotor to the side of the wheel-mounting flange finished to fine surface roughness, it is possible to suppress runout of the brake rotor.
Thus, troublesome runout adjustment of the brake rotor at the car assembling factory becomes unnecessary.
In the above arrangement, by adjusting the surface roughness of one side of the wheel-mounting flange to which the brake rotor is fixed to 3 Ra or under, and the surface roughness of the other side to 3-6 Ra, good results are obtained. The surface roughness of 3 Ra is obtainable by forming the wheel-mounting flange by primary cutting and then performing secondary cutting on the brake rotor fixing surface on one side thereof.
It is advantageous because of lesser number of the parts to form raceways directly on the outer periphery of the inner member or the inner periphery of the outer member.
The present invention is applicable to both wheel bearing assemblies for a driving wheel and those for a non-driving wheel.
According to the present invention, after a cylindrical portion on the side of the raceways of the outer member or the inner member provided with the wheel mounting flange has been formed by turning, the brake rotor fixing surface of the wheel mounting flange is finished by cutting with the cylindrical surface of the cylindrical portion as a reference.
By finish-cutting the brake rotor fixing surface with the cylindrical portion on the raceway side as a reference, the brake rotor fixing surface can be accurately worked relative to the rotation axis of the inner member or outer member, so that it is possible to suppress the runout of the brake rotor fixing surface to a minimum.
Thus, no troublesome runout adjustment of the brake rotor at the car assembling factory is necessary.
Also, by finishing the roughness of the brake rotor fixing surface finely, i.e. to 3 Ra or under, it is possible to further suppress runout of the brake rotor.
The surface roughness of 3 Ra or under may be achieved by forming the wheel mounting flange by primary turning and then performing secondary turning on the brake rotor fixing surface on one side while rotating the inner member or outer member with the raceway as a reference.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: